Steering colmun shaft

If you are concerned you could melt some plastic and pour it in the holes!

I would devise some sort of backer for the holes inside the shaft.

I believe the plastic gets injection molded into the holes while the shafts are in a jig to do 2 things,

1. Keep the inner and outer 1/2s seperate by a thin layer of plastic to make the slide
2. Act as a lock so the 1/2s dont move relitive to each other.

i suspect during assy havings the 1/2s locked together made it easier to assemble the cars.

On a Ford column I once had I substituted a deferent lower shaft that was longer, the Ford's were not locked together, the plastic just acted as a slide